In conventional techniques for displaying data in the form of a graph, the display width or graduations for a graph display area are preset such that a graph of the data can be displayed within the graph display area. At this time, when some of the data goes out of the preset display width, the corresponding part of the graph will not be displayed in the graph display area. Another problem is that depending on fluctuations of data contents, the graph can become too small or too large, making it difficult to grasp the characteristics of the graph.
In cases where biological information such as blood pressure or electrocardiogram, process values from a plant, or the like are displayed as a display object of a graph, such graph display needs to be monitored in real time. Therefore, a technique is particularly required that allows appropriate presentation of a graph within a display, irrespective of fluctuations of data contents.
In order to satisfy such requirements, a technique has been proposed that allows a calculator with a graph display function to change (enlarge, contract) its display width (range) to another, using central coordinates in a display screen or coordinates of a pointer on the display screen as a reference (for example, see Patent Document 1). Patent Document 1: JP-A-SHO 62-186346 (FIG. 2)
With the technique as described above, an enlargement or contraction process can be performed on a graph, using the central coordinates or the position of the pointer in the display screen as a reference. This allows the graph to be displayed in an appropriate size and facilitates grasping of the general tendency of data in the display screen.
However, in cases of graph display of biological information or process values, grasping of certain variation patterns of data may be given priority over grasping of the general tendency of the graph in the display screen. For example, in cases of graphs with periodicity based on data representing sinusoidal, voltage or current, waveforms indicating a cyclic signal from a machine, electrocardiographic data, or the like, portions representative of the periodicity may often be more important to identify.